Various methods have been used in the prior art for retreading tires. One method comprises recapping the worn tire by a hot vulcanizing process, in which an uncured tread is applied to the buffed crown surface of the used tire casing, and the assembly is then vulcanized at a high temperature in an appropriate mold. There are certain disadvantages to this method, and a second method is presently in widespread use in the art. In accordance with the second method, a pre-molded, pre-vulcanized tread strip is bonded to the buffed crown surface of the casing by a so-called cold vulcanization process.
In carrying out the cold vulcanization process, the casing is first buffed to remove as much of the old tread as possible. The crown surface of the casing is then covered by a quantity of uncured rubber, or other bonding agent, and a strip of pre-molded, pre-vulcanized tread is then wrapped around the periphery of the casing, It is then the usual practice to enclose the assembly in a thin envelope which is usually composed of a rubber-like material.
The purpose of the envelope is to permit air pressure within the chamber to be applied uniformly over the tread surface throughout the curing process, without any tendency for the air pressure to extend into the annular space between the tread and casing, and which would tend to lift the tread from the casing and destroy the bond. The envelope also provides an effective escape route for air that might be trapped in the annular space between the tread and the casing, such air being forced out of the annular space when pressure is first applied during the cure cycle of the cold vulcanizing process. For the latter purpose, an appropriate bleeding means, such as nylon mesh, or the like, is interposed between the envelope and the tread/casing combination.
An important objective of the present invention is to provide improved apparatus, whereby the aforesaid envelope may be conveniently held and sealed in position around the tread/casing combination to provide a perfect seal which is independent of tire pressure of spring tension. As stated briefly above, the apparatus of the invention includes annular pressure members which are removably mounted on the rim which supports the casing, and which serve to seal the envelope directly to the outer surfaces of the rim flanges. Hinged bolts and wing nuts are mounted on the rim to provide a simple and quick means for mounting the annular pressure members in place, and for permitting the pressure members readily to be demounted from the rim.
Guides are provided on the rim to assure that the annular sealing members will be properly centered with respect to the casing. The apparatus of the invention is advantageous in that its envelope sealing capabilities do not depend on tire pressure or spring tension. The apparatus of the invention assures that the envelope will be held firmly under all conditions, with a perfect seal being established throughout all the interior envelope area.